1. Field of the Invention
The invention relates to structural elements used in construction and infrastructure, and more specifically to composite structural elements having a fibrous layer impregnated with epoxy, preferably adhered to a foam core.
2. Description of Related Art
Traditional composites gain much of their strength by the type of fibers (carbon fiber, Kevlar, fiberglass, etc.) that are included in the composite structure. For many composite applications, such as building materials, these fibers prove to be too costly and limit their use.
Due to cost constraints, there are no composite-based structural insulated panels on the market. Traditional structural insulated panels are made from either wood or steel structures that are insulated by either polyurethane or polystyrene. The insulating material is “sandwiched” between two layers of the wood or steel outer skin. Bonding between layers is done with various glues.
These traditional composites use expensive fiber materials such as those mentioned above to achieve high strength. This limits their use in cost-sensitive industries such as building and infrastructure. Other panel systems used for walls, roofs and floors are comparable in cost but have inherent material issues such as rotting, corrosion, and delamination between the insulating core and the exterior skins. In addition, other panel systems require additional layers to be added to their exterior before finishing the wall with stucco or mud.
One excellent composite-making method is described in U.S. Pat. No. 6,117,376 to Merkel, the instant inventor, and which is assigned to the instant assignee; the teachings of U.S. Pat. No. 6,117,376 are incorporated by reference herein. In this method, a mold is created and carbon fiber layers or skins line the inside surfaces of the mold halves. The carbon fiber layers are wetted with heat-curable epoxy, and the mold halves are closed together to form an interior cavity having an opening. Exothermic foam is introduced into the mold cavity in an amount so as to overfill the mold. The foaming material expands and heats up, causing the heat-curable epoxy to cure. Since an abundance of foam is provided, excess foam spills out of the opening in the cavity, but because the foam expands so rapidly, the pressure inside the mold causes the carbon fiber layers to be pressed flat against the inner surfaces of the mold. In addition, the epoxy cures (from the heat generated by the exothermic reaction of the foam) and causes the carbon fiber layers to stick securely to the internal foam. The resulting composite is exceptionally strong and can be created in substantially any shape. However, while the method of manufacture is easy and inexpensive and can even be performed on the construction site, as mentioned above, the carbon fiber layers are too expensive to make the resulting product a practical building material.
In addition to new construction, traditional infrastructure repair is lacking for similar reasons. For example, in repairing a columnar support of a bridge substructure, the conventional approach is to weld pre-rolled steel panels to the exterior of the column, and then backfill the structure with concrete. The problems with this approach are manifold. For one, the steel and concrete are extremely heavy and thus have high shipping costs. In addition, in performing this retrofit, the footing of the column must be replaced, and the roadway above must be closed. Finally, the process takes an unacceptably long time to complete.
Accordingly, there is a long-felt need for a building structure and material that is light weight, easy to manufacture, and cost-efficient as well, that can be used for both new construction as well as for repair purposes.